sweeping aside a documentation stumbling block for new people

[bitemyapp]

Cheers :)

[bitemyapp]

Also, please rebuild and push the documentation afterward, Hackage docs are broken for current version. New people won't know to walk the version back a notch.

See here for example of manual doc pushing:

https://github.com/bitemyapp/bloodhound/blob/master/Makefile#L27-L29

[lpsmith]

Would it make more sense to use :: IO [Only Int]? At least, that's what I would do...

[bitemyapp]

@lpsmith Point of the change is to make the documented example "just work" for new people as it currently doesn't, I just tried what you suggested and the following happened:

λ> query_ conn "select 2 + 2" :: IO [[Int]]
[[4]]
λ> query_ conn "select 2 + 2" :: IO [[Only Int]]

<interactive>:6:1:
    No instance for (Database.PostgreSQL.Simple.FromField.FromField
                       (Only Int))
      arising from a use of ‘query_’
    In the expression: query_ conn "select 2 + 2" :: IO [[Only Int]]
    In an equation for ‘it’:
        it = query_ conn "select 2 + 2" :: IO [[Only Int]]

[lpsmith]

You have an extra list type constructor, that should be only one set of brackets, not two.

Only is a 1-tuple introduced by mysql-simple and adopted by postgresql-simple, it's FromRow instance looks for only one column of a given type whereas [a]'s instances consumes all of the remaining columns, and the postgresql type of every column must be compatible with a's FromField instance. (Although they need not all be the same postgresql type.)

[bitemyapp]

@lpsmith I see now, I'll change accordingly.

λ> query_ conn "select 2 + 2" :: IO [Only Int]
[Only {fromOnly = 4}]

But you should note that I didn't figure this out from the documentation. People cannot derive this stuff themselves if they didn't write the library.

[bitemyapp]

@lpsmith changed per recommendation, thanks :)

[lpsmith]

I don't doubt the documentation could be better, and I do very much appreciate having a beginner look at this. But I would point out that despite a fair number of users, I don't get that many questions via email or IRC, and Only is documented